1. Field of the Invention
The present invention relates to a battery pack and a protection method thereof.
2. Description of the Related Art
In general, a battery pack includes a plurality of battery cells, a charging switch to prevent the battery cells from being overcharged, a discharging switch to prevent the battery cells from being over-discharged and a control unit to control the charging switch and the discharging switch.
The control unit senses voltages of the battery cells, so that it turns off the charging switch to stop charging if the battery cells are overcharged and the discharging switch to stop discharging if over-discharged.
If the battery pack is left alone for a long time, it continues to decrease in voltage due to a self-discharging phenomenon that discharges on its own by three to five percents each month, even though the discharging switch is turned on to stop discharging. For instance, in a lithium-ion battery cell or a lithium-polymer battery cell, the discharging switch is turned off to stop discharging if a voltage of the battery cell comes to approximately 2.0 to 3.0V. However, if the battery cell is left alone in such a state for a long time, the voltage of the battery cell may drop to approximately 0 to 1.0 V.
When the battery cell is discharged to approximately 0 to 1.0 V as described above, a copper used in forming a negative electrode collector may be melted. That is, the cooper is eluted from the negative electrode collector, so that a negative electrode and a positive electrode are electrically connected to or with each other, thereby causing a short circuit. Under this state, if the battery cell or/and pack begins to charge, a large amount of heat may be generated between the negative electrode and the positive electrode, which are short-circuited, and thus the battery cell and/or pack may explode or ignite.